1. Field of the Invention
The invention relates to burner systems and, in particular, to burner systems employing electrically ignited pilot burners for controlling the operation of main burners.
2. Description of the Prior Art
The prior art, as exemplified in U.S. Pat. Nos. 1,844,959, 2,630,860, 2,705,531, 3,236,448, 3,312,396 and 3,692,239, contains many burner systems including burner systems employing igniter operated pilot burners which control flame valves between a fuel control and a main burner. Generally, the prior art systems utilize flame valves operated by mercury containing sensing bulbs which are limited to a maximum operating temperature in a range of about 398.degree. to 427.degree.C. Also, many prior art burner systems are unduly complex in that they employ many relatively expensive components to produce the safety and desired operating characteristics of the burner system.
Also, the prior art, as exemplified by U.S. Pat. Nos. 2,627,911, 2,787,130, and 3,405,999, contains many thermally operated valves including flame sensing valves for burner systems utilizing gas charged bulbs with adsorbent, activated carbon materials, such as activated charcoal, for operating the valve. Attempts to employ such activated adsorbent material containing flame valves on a large scale in burner systems have generally met with failure; activated carbon materials do not generally produce sufficient increase in volume or pressure change per degree temperature change necessary to operate the burner systems at temperatures associated with flame sensing to warrant the added cost of the carbon materials; and different batches of activated materials exhibit widely varying adsorbent properties at flame sensing temperatures which make reliable operation of burner systems at a predetermined temperature difficult to attain. Gas-fired ovens have generally required liquid-vapor actuated valves, such as mercury actuated valves, to produce the degree of movement of a valve closing member at the particular range of temperatures involved with the flame; however, such liquid-vapor valves are limited to operation at temperatures near the boiling point of the liquid.
Many adsorbent carbon materials are described in the pior art, including polyvinylidene chloride and polyvinylidene fluoride, as exemplified by U.S. Pat. Nos. 1,744,735, 3,258,363, 3,442,819, 3,516,791, and a publication (USSR Academy of Sciences, M. M. Dubinin, "Thermal Treatment and Microporous Structure of Carbonaceous Adsorbents", Proceedings of the Fifth Conference on Carbon, Vol. 1, 1962, pp. 81-87). Polyvinylidene chloride and polyvinylidene fluoride, in particular, have been recognized for their "molecular sieve" property, that is, their ability to adsorb certain gaseous materials, which have small molecular sizes and being incapable of adsorbing other gaseous materials which have larger molecular sizes.